JPH0834485B2 - GMSK quadrature synchronous detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a GMSK suitable for use in, for example, mobile communication.
(Gaucia minimum shift keying) Quadrature synchronous detector.

2. Description of the Related Art A conventional GMSK quadrature synchronous detection device of this type has a configuration shown in FIG.

That is, in FIG. 2, 1 is a clock recovery circuit, 2 is a multiplier connected to the clock recovery circuit 1, 3 is a low-pass filter (LPF) connected to the multiplier 2, and 4 is its LPF3.
A voltage-controlled oscillator (VCO) connected to VCO5, a π / 2 phase shifter connected to the VCO4, a multiplier connected to the VCO4, a multiplier connected to the π / 2 phase shifter 5, 8 is a multiplier connected to the multiplier 2, 9 is a low-pass filter (L
PF), 10 is a low-pass filter (LP) connected to the multipliers 7 and 8.
F) and 11 are demodulators connected to LPFs 9 and 10.

Assuming that the modulated wave is cos (wct + φ (t)), the carrier on the transmitting side is cos (wct), and θ is the phase difference between the carrier on the transmitting side and the reproduced carrier on the receiving side, the output of VCO4 is cos (wct +
θ) and the components higher than the angular frequency Wc are cut by the LPFs 9 and 10, as the input signal to the multiplier 8, cos (φ (t)
+ Θ) and sin (φ (t) + θ) are obtained. Therefore, the output signal of the multiplier 8 is sin (2φ (t) + 2θ).

Where φ (t) is It is expressed by Is output, the output of the multiplier 2 is Is obtained, and only sin (2θ) is obtained by LPF3.

The VCO4 controls θ so that the output sin (2θ) of the LPF3 becomes zero.

Thus, even with the conventional GMSK quadrature synchronous detection device,
The carrier wave on the transmitting side can be regenerated.

Problems to be Solved by the Invention However, in the above-mentioned conventional GMSK quadrature synchronizer, due to fading or the like, if there is a large phase change in the transmission line, there is no way to detect this, and as a result, the phase of the reproduced carrier wave, There is a problem that it cannot be changed in response to the large phase change, that is, the followability of the reproduced carrier wave is poor and the transmission error rate increases.

The present invention is to solve such a conventional problem, and to provide a GMSK quadrature synchronous detection device capable of speeding up the follow-up property of a reproduced carrier when a large phase change occurs in a transmission line. With the goal.

Means for Solving the Problems In order to achieve the above object, the present invention provides means for converting a received signal into two orthogonal baseband signals, and data from low frequency components of the two orthogonal baseband signals. A demodulator for decoding, a GMSK baseband modulator for generating a baseband signal of a transmission signal from the decoded data, and a baseband signal of this transmission signal are π / 2, π and 3 respectively.
π / 2 phase-shifting first, second and third phase shifters, low-frequency components of the two orthogonal baseband signals and GMSK baseband modulator, first, second and third phase shifters From the output signals of the first, second, third and fourth error detectors for detecting the phase shift error with each output signal of the detector and the output signals of the first, second, third and fourth error detectors The phase tracking amount of the carrier wave is 0,
A phase control device selected from π / 2, π, and 3π / 2 is multiplied by the low-frequency components of two orthogonal baseband signals, and the multiplication output is multiplied by the clock signal synchronized with the transmission data interval. Multiplying means, a voltage controlled oscillator for controlling the oscillation frequency by the low frequency component of the output of the multiplying means, and an output signal of the voltage controlled oscillator based on the output of the phase control device, 0, π / 2, π and 3π / 2. By providing a phase shifter that shifts only one of the two, it is possible to detect a large phase change and speed up the followability of the reproduced carrier wave.

Effect According to the present invention, a signal corresponding to the detection output is generated from the reproduced data string, and the phase difference from the detection output is calculated. This makes it possible to detect large phase changes,
The trackability of the reproduced carrier wave can be increased.

First Embodiment FIG. 1 is a schematic block diagram of a GMSK quadrature synchronous detection device which is an embodiment of the present invention.

In FIG. 1, reference numerals 21 and 22 are multipliers. 23 and 24 are low-pass filters (LPF), and LPF23 is applied to the multiplier 21 and LPF2.
4 is connected to the multiplier 22. 25 is a multiplier, LPF
It is connected to 23,24. 26 is a demodulator, LPF23,24
It is connected to the. 27 is a clock regeneration circuit for regenerating a clock signal synchronized with the transmission data interval.

28 is a multiplier, and the multiplier 25 and the clock recovery circuit
Connected to 27. 29 is a low-pass filter (LP) that passes the regenerated clock signal and the signal obtained from the detection output.
F) and is connected to the multiplier 28. 30 is a voltage controlled oscillator (VCO) controlled by the output of LPF29, and L
It is connected to PF29. Reference numeral 31 is a phase shifter for shifting the output of the VCO 30 and is connected to the multipliers 21 and 22 and the VCO 30.

32 is a reproduced carrier wave (VC
It is a phase shift control device that determines (controls) the phase shift to be added to the O30 output), and is connected to the phase shifter 31. 33,34,35,36
Is an error detector for obtaining the above-mentioned four types of errors, all of which are connected to the LPFs 23 and 24 and the phase shift control device 32. 37,38,
Reference numerals 39 are 3π / 2, π, and π / 2 phase shifters (three types of phase shifters). The 3π / 2 phase shifter 37 is the error detector 33, and the π phase shifter 38 is the error detector. At 34, the π / 2 phase shifter 39 is connected to the error detector 35. Reference numeral 40 is a GMSK baseband modulator that produces an in-phase component signal and a quadrature component signal corresponding to the detection output from the reproduced data string, and is connected to the demodulator 26, three types of phase shifters 37, 38, 39 and the error detector 36. Has been done.

Here, the three types of phase shifters 37 to 39 phase-shift each output (generated output signal) of the modulator 40. Also, the error detector
33 to 35 find the error between the outputs of the three types of phase shifters 37 to 39 and the detected output, and the error detector 36 finds the error between the output (generated output signal) of the modulator 40 and the detected output. In this way, the four error detectors 33 to 36 determine the four types of errors. From these four types of errors found,
The phase shift that the phase shifter 31 adds to the reproduced carrier wave (VCO30 output)
The phase shift control device 32 controls and determines.

 Further, the operation of the above embodiment will be described in detail.

In FIG. 1, the modulated wave passes through the multipliers 21, 22, LPFs 23, 24 and becomes two types of signals as in-phase components and quadrature components as detection outputs.

The two types of signals are multiplied by the multiplier 25. The multiplier 28 multiplies the two kinds of signals resulting from the multiplication by the recovered clock signal output from the clock recovery circuit 27, removes high frequency components with the LPF 29, and detects the phase difference θ between the carrier waves on the transmitting side and the receiving side. For sin (2θ). In VCO30, sin
Depending on the magnitude of (2θ), the phase difference operates to be zero.

On the other hand, the demodulator 26 reproduces data from the two kinds of signals, and the output when the carrier wave having the same phase as the transmitting side is detected from the reproduced data string is calculated (modulation device).
40).

Since a phase difference of nπ / 2 (n is an integer) occurs in a stable state between the reproduced carrier wave and the carrier wave on the transmission side, the calculation results in the case of the same phase are respectively π / 2 phase shifters 39, π phase shifter
38 and 3π / 2 phase shifter 37 are used to shift the phase by π / 2, π, 3π / 2. Then, the error detectors 33 to 35 find the error between the signal after the phase shift and the two kinds of signals as the detection output.

The obtained errors are compared with each other by the phase shift controller 32, and which of 0, π / 2, π and 3π / 2 the current phase difference is closest to is obtained. When a large phase change is applied to the transmission line due to fading or the like, if the change is π / 2 or more, the closest phase difference changes.

This change in phase difference causes the phase shift control device 32 to
An appropriate phase is selected from / 2, π, and 3π / 2, and the phase shifter 31 shifts the output of the VCO 30.

The output of the phase shifter 31 is used as a reproduced carrier wave,
Moreover, the output to the multiplier 21 and the output to the multiplier 22 have a phase difference of π / 2.

As described above, according to the above embodiment, a large phase change of π / 2 unit is detected, and when this is detected, the phase of the reproduced carrier wave is changed in π / 2 unit. On the other hand, a small phase change
Controlled by VCO30. As a result, when there is a large phase change, it is possible to quickly follow the reproduced carrier wave.

EFFECTS OF THE INVENTION The present invention, as is clear from the above embodiment, means for converting a received signal into two orthogonal baseband signals,
A demodulator that decodes data from low-frequency components of two orthogonal baseband signals, a GMSK baseband modulator that generates a baseband signal of a transmission signal from the decoded data, and a baseband signal of this transmission signal by π / First, second and third phase shifters for phase shifting by 2, π and 3π / 2, low-pass components of the two orthogonal baseband signals and a GMSK baseband modulator, first, second and third First, second, third and fourth error detectors for detecting a phase shift error with each output signal of the third phase shifter, and first, second, third and fourth
Of the output signal of the error detector of No. 2, the phase control unit that selects the phase tracking amount of the reproduced carrier from 0, π / 2, π, and 3π / 2 is multiplied by the low-frequency components of two orthogonal baseband signals. A multiplication means for multiplying the multiplication output by a clock signal synchronized with the transmission data interval, a voltage controlled oscillator for controlling the oscillation frequency by a low frequency component of the output of the multiplication means, and a phase control for the output signal of the voltage controlled oscillator. A phase shifter that shifts the phase by any one of 0, π / 2, π and 3π / 2 based on the output of the device is provided to detect a change in the phase difference between the carrier waves on the transmitting side and the receiving side, Since the phase of the reproduced carrier wave is changed in units of π / 2 when a large phase change is applied at, the followability of the reproduced carrier wave can be increased.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a GMSK quadrature synchronous detector which is an embodiment of the present invention, and FIG. 2 is a schematic block diagram of a conventional GMSK quadrature synchronous detector. 21,22,25,28… Multiplier, 23,24,29… Low-pass filter (L
PF), 26 ... Demodulator, 27 ... Clock recovery circuit, 30 ... Voltage controlled oscillator (VCO), 31 ... Phase shifter, 32 ... Phase shift control device, 33
~ 36 ... Error detector, 37 ... 3π / 2 phase shifter, 38 ... π phase shifter,
39… π / 2 phase shifter, 40… GMSK baseband modulator.

Claims (1)

[Claims] 1. A means for converting a received signal into two orthogonal baseband signals, a demodulator for decoding data from low-frequency components of the two orthogonal baseband signals, and a baseband of a transmitted signal from the decoded data. A GMSK baseband modulator for generating a signal and first and second phase shifts of the baseband signal of the transmission signal by π / 2, π and 3π / 2, respectively.
And a third phase shifter, low-frequency components of the two orthogonal baseband signals, and a GMSK baseband modulator, first,
First, second, third and fourth error detectors for detecting a phase shift error between each output signal of the second and third phase shifters, and the first, second, third and fourth error detectors. From the output signal of the error detector of 0, π / 2, π and 3π
A phase control device selected from / 2, multiplication means for multiplying low-frequency components of the two orthogonal baseband signals, and a multiplication output and a clock signal synchronized with a transmission data interval, and the multiplication A voltage-controlled oscillator for controlling the oscillation frequency by the low-frequency component of the output of the means, and an output signal of the voltage-controlled oscillator is 0 based on the output of the phase control device,
A GMSK quadrature synchronous detection device having a phase shifter that shifts the phase by any one of π / 2, π and 3π / 2.